Purification of dodecanedioic and undecanediotc acids



United. States 7 PURIFICATION OF DODECANEDIOIC UNDECANEDIOIC ACIDS Thomas R. Steadman, Waban, and John 0. H. Peterson,

.Jr., Medford, Mass, assignors to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts 3 Claims. (Cl. 260-537) This invention'relates to the production of chemicals and in particular to the purification of acids.

A principal object of the present invention is to provide a method for the purification of the dicarboxylic acids, undecanedioic and dodecanedioic acids. 1

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed disclosure.

U. S. 'Patents 2,614,122 and 2,365,290 illustrate the preparation of long chain dicarboxylic acids such as undecanedioic and dodecanedioic acids by the oxidative cleavage of hydroxylated fatty materials. These acids are particularly useful in the preparation of polyesters or when esterified as plasticizers for vinyl compounds. In these reactions, however, there are also prepared lower monocarboxylic acids obtained from the other portion of the molecule being oxidized; thus for example, in the oxidative cleavage of 12-hydroxystearic acidas illustrated in the above United States patents or in the oxida-tive cleavage of 12-ketostearic acid or esters thereof as illustrated in copending applications Serial No. 549,874, filed November 29, 1955, and Serial No. 521,618, filed July 12, 1955, there is produced undecanedioic, dodecanedioic, caproic and enant-hie acids. The relatively short chain monocarboxylic acids, such as caproic and enanthic may be effectively separated from the dicarboxy-lic acids by steam distillation. However, the stearic. acid present in the starting material is not afiected by the nitric acid and, being relatively involatile, is not removedby steam distillation and thus remains asan impurity in the dicarboxylic acid mixture. The present invention is directed to a novel process for purifying a mixture of dodecanedioic and undecanedioic acids by the removal of stearic acid therefrom.

The process of the present invention preferably comprises heating a solution containing aqueous acetic acid and a mixture of dodecanedioic and undecanedioic acids contaminated With stearic acid to a temperature on the order of the boiling point of the solution, removing the oily phase which separates during the heating, cooling the resultant clear, aqueous acetic acid phase, and recovering a high purity mixture of dodecanedioic and undecanedioic acids.

One specific detailed method of practicing the present invention is set forth in the following non-limiting example.

Example I A mixture of 5190 grams (57.6 moles) of 70% nitric acid, 13 grams of powdered copper and 5.19 grams of ammonium vanadate was placed in the reaction vessel decolorizing carbon, heated and filtered.

Patented Aug. 12, 1958 ice and heated to 78 C. Thereupon, 905.;grams (2.45 moles) of molten commercial (85% 'pure)-' methyl 12-hydroxystearate (the remaining 15% being stearic acid) 'was added-to. the. rapidly :stirred. reaction mixture at a temperature of 9095' C. over'a period of 50 minutes.- During this time water at --65 .C. was circulatedin a jacket surrounding the reactor. :The use of lower cooling Water temperatures was/avoidedin' fear. of freezing organic materials on the interior surface of the reactor. The reaction mixture was "kept at the reaction temperature for about 10 minutes after the addition of the methyl IZ-hydroxystearate .and'then discharged to an open-stainless steel vessel. Theimixture was cooled to 15 C. with stirringand the precipitated material filtered off. By reslurrying the filter cake with water the-precipitated acids were washed thoroughly, using a total of one .liter of water in four, portions; The Wet filter cake was then melted and theaqueous phasetwhich separated Was-discarded. The product at .this point consisted of a mixturejof enanthiq-caproic and stearic acids with the dodecanedioic .and undecanedioic acids. andweighed 800 grams when thoroughly dried.

The above product was subjected to a distillation with steam superheated to l20-125 C. to remove the volatile monobasic acids, enanthic and caproic; Temperatures much in excess of 125 C. for the superheated steam result in some decomposition of the mixture.

The residual non-volatile acids, stearic, undecanedioic and dodecanedioic acidswere recrystallized from about a 30% aqueous acetic acid'solution. Thus, the nonvolatile acids from two oxidation experiments, weighing 935 grams (consisting of about 90% dicarboxylic acids and about 10% stearic acid), were dissolved in 1000 ml. of acetic acid and treated with 50 grams of decolorizing carbon, heated and then filtered. The filtrate was diluted with 2000 ml. of water and this mixture heated to the boiling point (100 C.). An insoluble black, oily layer or phase weighing 103 grams was separated from the hot solution. The resulting clear, aqueous acetic solution was cooled to 20 C. to precipitate or crystallize out the dicarboxylic acids. The mixture was filtered and the filter cake obtained was redissolved in 1000 ml. of acetic acid and this solution treated with 53 grams of The filtrate was diluted with 2000 ml. of water and this mixture heated to 100 C; 24 grams of a black oily phase or layer which separated from the hot solution was removed. The resulting clear, aqueous acetic acid solution was cooled to 20 C. The white, crystalline mixcarboxylic acids were found to be retained by the decolorizing carbon. 127 grams (13. 6%) of stearic acid were recovered from the oily phases which solidified on cooling. 14 grams (1.5%) of the dicarboxylic acids remained in the mother liquor.

Although only aqueous acetic acid solutions of about 30% are illustrated, it is also possible to utilize aqueous acetic acid solutions of somewhat lower or higher concentrations. Increasing the acetic acid concentration much above 30% increases the solubility of the stearic acid in the solution. Decreasing the acetic acid concentration much below 30% causes more of the dicarboxylic acids to go into the oily phase.

The stearic acid contaminated mixture of dodecanedioic and undecanedioic acids may be adequately purifiediby rsubjectingit 1 to only one recrystallization with acetic, acid. .However best resultsareachieved when the impure mixture is subjected rto more than one recrystallization.

:Since :certain changes may be made in th'e above-procfissswithouttdeparting from the scope of the invention hereinrinvolved, ibis intended that all mattencontained inrthe .above description shall '-be.- 'interpreted a's illustrative: and DOtLiIl aliimiting sense! WhatJi's claimed is:

1. The'processrwhich comprises-dissolving a mixture of dodecanedioic .and undeca nedioic acids contaminated withstearic acidinau aqueous solution of aceticacid,

' sultan: clear, aqueous acetic .1 zation of the acids dissolved therein, recovering the heatingsaidsolutionvtoa temperature on the order of the boiling point tot vthe :solution, irernovin'g the oily phase which separateszjfromcthe hot:-s'olution, cooling the resultant clear, waqueous: ace'ti'c acid-phase, and recovering ahi'gh :purityxmixture ofrdodecanedioic and undecanedioic acids.

2. The-process which comprises dissolving a mixture of dodecanedioic andcund'ecanedioic acids contaminated withstearic a'cidin an-aqu'eous solution ofacetic acid, heating said solution to a temperature on the orderof the boiling point of .the solution, recovering the .oily phase which. separates from; thehot solution, vcoolingthe reacid phase to cause crystallicrystallized acids, dissolving said recovered acids in aqueous acetic acid, heating said solution to a temperature on the order of the boiling .point of the solution, removing the oily phase which se arates from the hot solution, coolingthe resultant clear, aqueous acetic acid phase, and recovering a highpurity mixture of dodecanedioic and undecanedioic acids.

3. 'The proeess 'which comprises dissolving a mixture of dodecane'dioic-and undecanedioic acids contaminated with stearic acid in about a aqueous solution of acetic acid, heating said solution to a temperature on the order. of C.; removing the oily phase which separates from the ;h0t'='solution,' cooling the resultant clear aqueous acetic acid phase, and recovering a high purity mixture of dod'ecanedioic and 'un'decanedioic acids.

ReferencesCited in the file of this patent UNITED STATES KPATENTS 2,203,680 Ellin-gboe June 11, 1940 2,731,495 Emslie Jan. 17, 1956 2,777,865 Logan Jan. 15,- 1957 

1. THE PROCESS WHICH COMPRISES DISSOLVING A MIXTURE OF DODECANEDIOIC AND UNDECANEDIOIC ACIDS CONTAMINATED WITH STEARIC ACID IN AN AQUEOUS SOLUTION OF ACETIC ACID, HEATING SAID SOLUTION TO A TEMPERATURE ON THE ORDER OF THE BOILING POINT OF THE SOLUTION, REMOVING THE OILY PHASE WHICH SEPARATES FROM THE HOT SOLUTION, COOLING THE RESULTANT CLEAR, AQUEOUS ACETIC ACID PHASE, AND RECOVING A HIGH PURITY MIXTURE OF DODECANEDIOIC AND UNDECANEDIOIC ACIDS. 